Bleaching fibers



Patented Jan. 9, 1945 UNITED STATES PATENT OFFICE to Buffalo Electro-C Tonawanda, N. Y.

l remical Company, Inc.,

No Drawing. Application January 30, 1943,

Serial N 0. 474,183

Claims.

This invention relates to a method of bleaching textile fibers and more particularly to the bleaching of cellulosic textile goods that contain portions dyed with dyes not fast to usual peroxide bleaching solutions, as, for instance, naphthol dyes.

Goods made of textile fibers of vegetable origin containing portions dyed with naphthol dyes have, heretofore, been bleached with chlorine bleaching processes rather than with peroxide bleaching processes since it is well known that naphthol dyes are not fast to the ordinary peroxide bleaching baths at the usual conditions of treatment 'and involving the normal bath compositions generally ncountered in kier bleaching.

Recently, however, goods containing naphthol dyed portions have been successfully bleached by immersion in special bleaching bath compositions and under controlled operating conditions. Best results were obtained in this method by the employment of peroxide solutions containing dyeconditioning agents rendering the dye fast. Due to the insolubility of these dye-conditioning materials a portion of the dye-conditioning agent may become physically entangled with the textile fiber which condition may require more than normal washing for correction.

It is an object of the present invention to provide a method of bleaching goods containing naphthol dyed fibers by the employment of peroxide bleaching solutions without the necessity of using dye-conditioning agents.

As a corollary it will be understood that undyed fabrics, as well as fabrics portions of which are dyed with dyes normally fast to peroxide, may, at the same time, be bleached with fabrics containing portions dyed with dyes not normally fast to peroxide, such as the naphthol dyes, thus permitting the establishment in a given plant of a standard bleaching operation capable of handling all types of goods. The result is the elimination of the chlorine bleaching operation set up especially for the treatment of naphthol dyed goods in plants which normally bleach all other classes of goods with the more desirable peroxide bleach.

It is a further object of the invention to provide a peroxide bleaching method for bleaching goods containing portions dyed with dyes not fast under normal peroxide treatments.

It is also an object of the present invention to provide a method for bleaching goods containing portions dyed with naphtol dyes under conditions wherein there is no circulation of bleaching solution in or through the goods.

In accordance with the present invention the textile fibers, as, for instance, cotton, linen, and the like, which contain portions dyed with dye stuffs, such as naphthol dyes, not fast to the usual peroxide treating operations, are dampened with a solution containing peroxide. The goods are dampened in any suitable fashion, as, for instance, by spraying whereby the amount of the solution in relation vto the fiber constitutes less than and in general about 50% to 90% of the dry weight of goods. That is to say, for each one part by Weight of fiber 0.50 to 0.9 part by weight of the solution are employed upon the fiber. In practical plant operation the fiber is dampened or impregnated with this amount of solution by immersing the goods in the solution for a period of time sufficient completely to wet the goods and thereafter eliminating the excess solution by passing the goods through squeezer rolls or by centrifuging them. The goods are then bleached at an elevated temperature at of above the boiling point of Water and under conditions where the ratio of liquid to fiber does not increase. In general the bleaching operation will be performed in any conventional steaming equipment, as, for example, the Well known Becco form of jay chute wherein convective vapor is directed into and around the goods packed in the jay chute, although any conventional steaming equipment may be employed.

Since in this operation it is desired to maintain the liquor ratio, that is, the ratio of the weight of liquid on the fiber to the weight of the dry fiber, less than about 0.9, the temperature within the jay chute is maintained at 212 F. or above to prevent condensation of steam on the goods. To this end the convection medium is preferably superheated steam although humidified air of above about 212 F. may also be employed. Depending upon the history of the goods and the Weight and type of fabric, the steaming operation may require from about 15 minutes to several hours, although in general good results are obtained in about 45 minutes to one'hour. Where continuous operation is desired the goods are fed into a jay in continuous fashion, passed therethrough in bulk where the hot goods are bleached and are thereafter continuously withdrawn from the jay. The goods are then washed and finished.

Although hydrogen peroxide is the preferred bleaching ingredient of the bleaching solution, peroxides other than hydrogen peroxide may be employed for this purpose, as, for instance, the

alkali metal peroxides, the alkaline earth metal peroxides, m was persilicates, percarherein as peroxides.

. bonates and other percompounds which produce hydrogen peroxide in solution, all designated The quantity of peroxide 1 employed will of course depend upon the type of 0.75 volume, or for very resistant goods it may be 3 volume.

In addition to the peroxide, the bath contains an alkali in amounts sufficient to produce the desired alkalinity but insumcient in quantity to raise the pH to the figure employed in normal peroxide bleaching. In accordance with the present invention the alkalinity of the bath should be considerably below the pH of about 10.8-41.0 of the normal alkaline peroxide bleaching solutions. In the present invention the pH of the solution should be in the neighborhood of 8.5-9.5. To produce the desired alkalinity it is suggested that somewhat mild alkalies be used, such as sodium pyrophosphate, di-sodium phosphate, sodium tetraphosphate, sodium bicarbonate, certain amino compounds, and the like. Since a mild buffering action is desirable, the pH is adjusted with weak acids or acid salts.

Where the goods are made of fibers that are quite motey and have not been preliminarily treated, the bleaching operation is best performed by first subjecting the goods to a preliminary cleaning operation to soften and loosen the motes. This preliminary cleaning operation must be of a type in which the detergent chemicals do not cause the naphthol dyes to bleed and crock off. In accordance with the present invention, therefore, the goods are padded with from 50 to 150% of an alkaline solution containing a peroxide and permitted to stand in the padded condition for a time sufiicient to soften and loosen the motes and at a temperature and alkalinity insuificient to produce bleeding and crocking of the dye. In general, steeping of the padded goods is performed at temperatures below about 125 F.

The padding solution is advantageously made of any peroxide and any alkali normally employed in cold padding operations, that is to say, caustic soda, soda ash, pyrophosphates, and the like, to which, if desired, soluble silicate, such as sodium silicate, may be added in stabilizing quantities.

As an example of a solution eminently suited for the performance of the preparatory cleaning operation, the following formulation is given as purely illustrative of the invention but not definitive thereof.

In 100 gallons of solution:

Pounds Silicate of soda (42 B.) 25

Caustic soda 6 Hydrogen peroxide-100 volume 18 Motey gray huck toweling containing a striped center dyed with naphthol dye was impregnated with 90% of the above solution and laid down at room temperature in bins over night. The goods were thereafter washed with hot and cold water and were then dampened with a bleaching solution of the following formulation:

Pounds Glacial acetic acid 0.35 Sodium pyrophosphate 3.8

Hydrogen peroxide100 volume 18 Water sufiicient to produce 100 gallons solution.

to the goods, the temperature in the chute being maintained at 214 F, in order to prevent deposition of moisture condensation on the goods. The goods were maintained in the chute for 60 minutes prior to discharge, were then removed and were washed and finished. The goods were found to be free of motes, free of crock marks and the red center stripe was not changed in shade and had not bled into the white background.

The pH of the treating solution and of the goods as padded therewith was initially 8.7 and had fallen to 7.2 when discharged from the chute.

Another sample of the same piece after the above preparatory cleaning was impregnated with the above bleaching solution to 105% of its weight and steamed at 214 F. in the same manner as above. The dye in this sample was badly crocked oif and so much bleeding had occurred that the cloth was unsuitable for use.

Other compositions can of course be used as the bleaching impregnant, for instance:

In 100 gallons of solution:

Pounds Sodium pyrophosphate 1.75 NasP4O13 0.85 H2O2-100 volume 18 Initial pH was 8.9 and the final pH was 7.0

As an instance of the employment of a salt, reacting acid in solution, the following formulation is given for 100 gallons:

Pounds Sodium pyrophosphate 3.9 MgSO; 1.0 H2O2100 volume 18 Initial pH of the clear solution was 9.0 and the final pH was 7.1.

It is believed that the great advantage obtained in steam bleaching goods containing portions dyed with naphthol dyes is dependent upon preventing any possible washing or circulating action of the bleaching solution. Thus by maintaining the weight of solution in the goods less than about and preventing condensation of steam upon the goods, there is insufficient surface water upon the goods to permit transfer of dye from the dyed portions to the undyed portions thereof.

From the above it will be seen that the present invention provides a method of bleaching goods dyed with naphthol dyes in a, rapid and expeditious manner, with a minimum consumption of energy and chemicals and with the production of goods in which bleeding and crocking are eliminated and wherein the finished goods may be associated and laundered without fear of bleeding.

What is claimed is:

1. The method of bleaching cellulosic goods containing portions dyed with naphthol dye which comprises heating the goods dampened with less than about 90% of their weight of an alkaline peroxide bleaching solution of a pH less than 9.5 in an atmosphere containing steam while preventing condensation of any substantial amount of steam from said atmosphere upon the goods.

2. The method of bleaching cellulosic goods containing portions dyed with naphthol dye which comprises impregnating the goods with 65 to 90% of their weight of an alkaline peroxide bleaching solution of a pH less than 9.5 and thereafter steaming the goods at a temperature above 212 F. until the desired degree of bleach is obtained.

3. The method of bleaching cellulosic goods containing portions dyed with naphthol dye which comprises impregnating the goods' with 65 to 90% of their weight of an alkaline peroxide bleaching solution of a pH less than 9.5 and thereafter treating the goods with superheated steam until the desired bleach is obtained.

4. The method of bleaching cellulosic goods containing portions dyed with naphthol dye which comprises impregnating the goods with 65 to 90% of their weight of an alkaline peroxide bleaching solution of a pH less than 9.5 and thereafter heating the goods while maintaining the weight of liquor between 65 to 90% of the weight of the goods during said heating treatment.

5. The method of bleaching gray cellulosic goods containing portions dyed with naphthol dye and containing motes which comprises dampening the goods with an alkaline peroxide bleaching solution and permitting the goods to stand at a temperature below about 125 F. until the motes are softened, thereafter washing the goods and then dampening them with 65 to 90% of their dry weight of an alkaline peroxide bleaching solution of a pH of less than 9.5 and heating the so dampened goods in an atmosphere of steam while preventing condensation of steam from said atmosphere upon the goods.

ROBERT L. McEWEN. 

